Silicone rubbers have entered into use in a wide variety of applications because they have excellent heat resistance and cold resistance and a low compression set. However, silicone rubbers generally have poor oil resistance and are therefore unqualified for use in applications that require oil resistance, for example, as rocker cover gaskets, oil packings, valve stem seals, oil filters, seal rings, shaft seals, etc., in automobiles, other types of vehicles, ships, airplanes, etc. In particular, when silicone rubber is employed in regular or continuous contact with a mineral oil-based lubricating oil such as engine oil, etc., or low-viscosity oil or fuel oil, the silicone rubber swells and fissures or cracks develop in it during long-term service. In response to this, Japanese Patent Application Laid Open (Kokai or Unexamined) Number Hei 1-203467 (203,467/1989) has proposed a silicone rubber that is based on a dimethylsiloxane 3,3,3-trifluoropropylmethylsiloxane copolymer gum. This dimethylsiloxane-3,3,3-trifluoropropylmethylsiloxane copolymer gum corresponds to a dimethylpolysiloxane gum (a primary component of silicone rubber) in which the methyl groups have been replaced in part with 3,3,3-trifluoropropyl groups. However, this dimethylsiloxane-3,3,3 -trifluoropropyhnethylsiloxane copolymer gum does not solve the problems described above.
The inventors achieved the present invention as the result of extensive investigations directed at solving the problems described above.